Purifying Ig out of milk

Recently someone posted a request for experiments that could be used
for teaching. In the post was a request for info on extracting
Ig from milk.
George Mestecky is at UAB and has been working with IgA for years. I
got this protocol verbally from one of his techs.
When getting the milk, add PMSF and Soybean Trypsin inhibitor. Milk
may then be frozen until processed. If processed immediatly, still add
the antiproteinases.
Perform all steps under refrigeration.
Defat the milk by spinning at 10000 RPM for a while.
Decasseinate the milk by bringing pH to 4 with acetic acid. Allow to
stir for 1 hour, then spin hard and keep supernatant. Cassein will
come down in with Ig in a slat cut, so it needs to come out with
this acid precipitation.
Perform 50% ammonium sulphate salt cut. Ig will be in precipitate.
If you are just doing an ouchterlony all this may not be necessary.
Steve Holland